Factory Five Racing Mk4 Roadster Assembly Manual page 485

In order to increase the flow of air above 5000 rpm, upgrade from the stock mass air sensor.
Aftermarket 70 mm or 75 mm mass air units are an excellent choice and have proven effective. If the
mass air meter is changed make sure it is calibrated for the injectors you are using or you will have to
change the injectors too. Pro-M or Ford Motorsport meters work the best. Usually the mass air meter is
larger than the throttle body.
Fuel Injectors
Stock 87-93 Mustang size: 19lb/hr.
The stock injectors are good for exactly that, a stock engine. If upgrading parts, step up to 24 lb/hr
injectors. They are good up to about 400hp. Make sure that you have the mass air sensor calibrated to
the injectors you use.
Upper Intake
The next logical step for breathing is a more free flowing intake manifold. There are a number of
intakes available from different companies (e.g. Edelbrock, Trick Flow). Ford also makes a good
intake, the cast 1993 Cobra intake from Ford Racing.
Heads
The 5.0L Mustang aftermarket is full of aluminum and cast iron heads for the small block Ford. Our
favorites are the Edelbrock Victor Jr. and the Trick Flow aluminum heads. These both flow very well,
have stock exhaust port heights which allows the use of our headers and not only give you extra
horsepower but also remove 50 lbs. in the process.
Cams
If you need to pass emissions testing, use a cam with a CARB number. We like the Ford E303 cam.
We have used it with success in our racecars both naturally aspirated and in boosted applications. If
building a more radical engine, match the cam to the combination.
Headers
Stock 1987-1995 Mustang: 1½" OD
We've found that the Mustang factory headers work well for the stock engine. If you want to go to an
aftermarket set, the 1⅝" MAC shorty unequal length headers or Ford Racing 1⅝" unequal length
headers fit as bolt on parts. They will reward you with an approximate 5-10 hp bump in the top end. All
aftermarket headers use mandrel (smooth consistent bends) bent tubing. The stock ones are not and are
restrictive on non-stock engines.
If using a 351W engine there are two options, use 351W engine swap headers from Ford Racing (M-
9430-A58) or MAC (E358692) or if smog/catalytic converters are not necessary, use our full length 4
into 4 headers.
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